The present invention relates to a circuit breaker, such as molded case circuit breaker and earth leakage breaker, and especially to an insulation device for a magnetic driving core which drives an electric arc toward an arc quenching device.
One of magnetic driving cores and its insulation device were described in the Japanese Laid Open Patent Publication No. H02-132716. This device is comprised of a U-shaped magnetic driving core having a pair of side arms and a connection base between the side arms and attached at an end of a stationary contact member which is bent back to a U shape. The device further comprises an insulation member which is integrally molded with cap parts for covering the side arms of the magnetic driving core, a bottom board part for covering the periphery of the stationary contact member except a stationary contact or the like, and a partition wall disposed between a moving contact member and an inner edge of a cut-off part of grid plates in an arc quenching device.
However, since the insulation member described in the Japanese Laid Open Patent Publication No. H02-132716 above has a shape of a cap, it has following problems;
(1) Since both inner and outer surfaces of the side arms of the magnetic driving core are covered with the cap parts of the insulation member, the side arms including the insulation member are thick. Consequently, if it is attempted to ensure space for right and left side arms wide enough to facilitate moving in and out of a moving contact member, there is a problem that the thickness of the magnetic driving core is limited. Therefore, a satisfactory performance of magnetic driving can not be obtained.
(2) Since the thickness of the cap part of the insulation member is also limited because of the same reason as described above, a satisfactory performance of insulation can not be obtained.
(3) The insulation member in the form of a cap requires a complex mold and a high cost, and work for covering the cap on the side arms is of low workability and requires long working time.
In viewing the foregoing problems, an object of the present invention is to provide an insulation device for a magnetic driving core of a circuit breaker with a satisfactory insulation performance, wherein the thickness of the magnetic driving core is less restricted, a molding is simplified, and a mounting workability is improved.